1. Technical Field
An aspect of the present invention relates to an image recording apparatus, which is capable of recording an image on a recording medium being carried by a conveyer unit. More specifically, the present invention relates to control of a rotation rate of a driving roller in the conveyer unit of an image recording apparatus.
2. Related Art
An image recording apparatus, such as a printer, a copier, and a facsimile machine, often includes a conveyer unit to convey a recording medium (e.g., sheets of paper) and a recording unit to form an image on the recording medium being conveyed by the conveyer unit. The conveyer unit may include a pair of conveyer rollers, which nip the recording medium in between and convey the recording medium toward the recording unit, and a pair of discharge rollers, which nip and convey the recording sheet with the image formed thereon to an outlet of the image recording apparatus. The discharge roller pair may be arranged in a downstream position with respect to the conveyer roller pair along a direction of conveyance of the recording medium. Each of the roller pairs may include a driving roller, which is rotated by driving source from a driving motor, and a driven roller, which is arranged in an opposite position from the driving roller to be driven according to the rotation of the driving roller. The recording medium is nipped between the driving roller and the driven roller to be carried as the driving roller rotates in a predetermined direction.
When the image is formed on the recording medium in the image recording apparatus, recording agent or colorant adheres onto a surface of the recording medium to form the image. Due to the adherence of the colorant, conditions (e.g., wetness) of the recording medium tend to be different between before and after the image forming operation. Therefore, the recording medium with the printed image may not be carried by the discharge rollers similarly to the unprinted recording medium being conveyed by the conveyer rollers. In other words, if the recording medium with the printed image is carried by the discharge roller pair in a same rotating setting as a rotating setting of the conveyer roller pair, the recording sheet may not be carried accurately in a preferred conveying rate.
More specifically, in a downstream section along the conveying path in the image recording apparatus with respect to the recording unit, the recording medium is nipped by the discharge roller pair to be conveyed further toward a most downstream section (i.e., the outlet) of the image recording apparatus. Therefore, when a part of the recording medium with the image formed thereon reaches the discharge roller pair, the image-formed part of the recording medium is nipped by the discharge roller pair. In other words, the colorant forming the image may be nipped by the discharge roller pair together with the recording medium. Thus, conditions in the recording medium are different between the image-formed and a part without any image due to the adherence or wetness of the colorant. In this regard, friction force caused in between the discharge roller pair with the image-formed part of the recording medium tends to be different from friction force caused in between a part of the recording medium with no image.